A lot of paleo thinkers seem to be rather sceptical of plants by default, preferring to 'eat food that can't defend itself after it's dead,' and assuming that plants are essentially out to get us, using whatever chemical means they can to stop us eating or fully digesting them. At the same time, many paleos think that select fruits and vegetables can be part of a healthy paleo diet and indeed part of the optimal paleo diet.
The historical evidence is much debated over, modern day hunter gatherer diets seem mixed. What I'm interested in working out is which plant foods- if I'm going to eat any at all- would be the safest candidates for staples of my diet. Tubers are a natural suggestion, but potatoes are related to nightshades and contain glykaoalkaloids, sweet potato contains cyanogenic glycosides. Leafy greens like spinach might seem to be a natural foodstuff that would be plentiful and easily gatherable throughout our evolutionary past, but they are full of oxalate and rubiscolin. Crucifers like cabbage, brocolli, kale etc are notoriously healthy, but are goitrogenic. Most fruits seem safer, but on the other hand are far more full of fructose, one of the most anti-paleo substances there is.
So the main things to consider seem to be:
Obviously the thing that ultimately counts is the hard physiological analysis of each of the respective chemicals, but since the data here would be ludicrously expansive and detailed, I think a paleo perspective on- what would we actually have evolved to eat?- is particularly useful.
The online paleo community is really hating on fruit these days, but it is the one plant that seems to want you to eat it. It does not, as you say, try to defend itself after it's dead.
Here's a counterargument to the "modern fruit is nothing but candy compared to undomesticated fruit": http://donmatesz.blogspot.com/2010/03/paleo-basics-how-much-sugar-in-wild.html
Isn't all this paranoia over fruits and vegetables getting pretty ridiculous? I mean when was the last time someone keeled over from eating broccoli, their thyroids buckling from the overdose of goitrogens?
If you really think that the slightest presence of "toxins" in vegetables and fruits is going to kill you or even have a noticeable impact on your health, what about paleos who live in cities? Shouldn't you be running away screaming from the pollution in the air? I'd think the exhaust fumes you inhale everyday would be far worst than the solanine in potatoes or the oxalates in spinach (lead, benzene, etc.). Why not live on some isolated island with a herd of grass-fed cows free from the evil grasp of linoleic acid, and chock full of omega 3s, and a tidy garden full of friendly plants that were nice and considerate enough to have evolved into non-toxic food sources.
Honestly, some of the paranoid comments about plant toxins here are just as inane as the comments made about the benefit of phytochemicals/polyphenols, etc. (Oh my! Acai berry will scour my blood clean of them free radicals vs. ZOMG! That spinach is sure as hell gonna clog my ureter).
I like to think that, as a species as successful as us humans, we are not as frail and defenceless against a couple of plants, which nobody in their right mind would call harmful, as is made out to be by some people here.
Quote from PaNu (I might be quoting out of context..but..):
"Part of this is philosophical as well, applying the 80/20 rule to health. I think the idea that one should micromanage dietary constituents based on speculative reasoning about magic special compounds is not only wrong, it is a big waste of time. There are many other things to occupy your time with.
Counting, measuring, weighing and titrating food and and researching supplements and special foods? I have zero interest in that, as I'd rather practice my guitar or read a good book."
It works both ways. How different is our obsession over plant toxins from the madness over magic compounds?
from what I'm seeing on Goitrogen, cooking the veg + adding saturated fat and possibly salt as a source of iodine = nothing to worry about (saturated fat, coconut and avocado all have the opposite affect of Goitrogen foods)
of course you have to remember this: anything in large enough amount is and can be poison. Often the same thing in small or moderate amounts is safe (e.g. water etc).
so for most things you eat it goes from negligible, to good for you, to safe, to possibly problematic/allergenic, to toxic, to silliness/madness/death.
fructose in small amounts (or spread out over a month or year) isn't going to be as dangerous as eating a whole jar of honey all at once, concentration and your body's ability to deal with it will be the issue for that.
I personally go by this the only reasonable paleo principal if its nothing but bad I don't' eat it, if in small amounts or as part of a balanced diet (e.g. it will do more good than harm especially mixed with something else I'd eat with it anyway, like cooked broccoli with butter) its a non issue.
and besides we seemed to have evolved fire + cooking before agriculture so fermenting/storing/preserving foods + cooking them to make them more edible seems to have a much longer evolutionary pairing with us than most agriculture centered foods.
I filter food choices through the Paleo lens, that's for certain. Fruit in particular is problematic for me. Likely a human of N. European descent as myself, would have had scarce access to fruit. Certainly NOT the modified/selected hyper-large, hyper sweet fruit of today, and in no where near the abundance nor variety. Frankly, neither would equatorial descendants!
I do not attempt to recreate our Paleolithic past! As Kurt Harris at PaNu blog points out, just use Paleo as a guide or filter to foods and lifestyle and activity and rest.
All the plants listed by David Moss have their drawbacks, for certain. Perhaps the intake of minor quantities of the anti-nutrients in various plants result in hormesis, a low dose of "poison" or stress that makes us stronger and more able to cope with other stressors. It is difficult to be so reductive in analyzing the troubling substances in various plants.
I suppose the question remains, what are the best plant foods? It may be easier to simply eliminate the WORST plants first (grains, legumes, many fruits perhaps?) and work backwards that way.
Based on what I've read about the most well-known toxins and potential "drawbacks" of each plant family (and as nicely summarised my David Moss in the body of his question), I have basically narrowed down my daily vegetable consumption to zucchini, squash/pumpkin, cucumber, carrots, celery, onions and garlic (and various spices). Not all at the same time, obviously.
These seem to be the least problematic from what I've read, but I'm continually adjusting as I learn more. Almost no fruits but occasionally berries. Occasionally mangetout beans for variety (although doubtful about the lectins...).
Sure must suck to be any species of herbivore on this planet, what with all those antinutrients and phytochemicals in thier diet! Bet they wish they'd evolved to eat meat!
Appologies for the sarcasm, just wish people wouldn't worry so much. Perhaps I just shouldn't go on this site.
I recently added the tuber, White Skinned Sweet Potato- The skin is where the benefits are found IN THIS VARIETY. It doesn't screw with my BG numbers. I eat one apple every fewe days when in season (Fall, not when the supermarket sells them) Some blueberries in summer. Both have to be Local. Most fruits are just sugar from a branch. Green leaf veggies are great, tomatoes. No root veggies- they are starch but Im diabetic so I have to be a little more selective.